BANGKOK (Reuters) - Environmentalists have forecast a grim future for planet Earth, predicting that droughts, heatwaves and hurricanes will become increasingly common and more severe if global warming is allowed to continue unchecked.

A coalition of eight of the world's largest conservation organisations said Russia's recent ratification of the Kyoto protocol on carbon dioxide emissions had given fresh impetus to the drive to cut global output of greenhouse gases.

However, they said more had to be done if the world's average temperature was going to stop short of a critical two degrees Celsius rise above its mean in the pre-industrial era.

"We collectively feel that if we were to go beyond the two degrees warming... we are bound for complete chaos and disaster on this planet," WWF director-general Claude Martin told a news conference on Thursday at the IUCN World Conservation Congress in the Thai capital.

"Everything must be undertaken to ensure that we do not pass beyond the two degree threshold of global warming because the results will be absolutely devastating, not just for nature but the whole of humanity," he said.

Australia and the United States are among those countries that have refused to ratify the protocol, putting a major dent in global efforts to cut carbon dioxide emissions.

The United States is by far the largest emitter of carbon dioxide, while Australia, which generates most of its electricity from coal power stations, is also a major polluter.

The Bush administration says the Kyoto pact is too expensive and is flawed because it doesn't commit major developing countries such as India and China to curb their greenhouse gas emissions. Australia says the pact is bad for industry.

Much of the private sector has also been slow to catch on to the need for greener, more efficient modes of power generation and transport, but Martin said the world community must not move at the pace of its slowest members if changes were going to happen.

"We should not be steered by those backward-looking fossil-fuelled companies, but should go forward with the progressive ones," Martin said.

In a joint statement with green groups such as Birdlife International and Conservation International, WWF drew particular attention to the impact of climate change in the Arctic, where temperatures appear to be rising at twice the rate of the rest of the world.

Up to 95 percent of the world's coral reefs, home to some of natures wierdest and most wonderful creatures, might also be dead from coral bleaching within 60 years if ocean temperatures continue to creep up, the group said.

Steve Howard of The Climate Group said it was impossible to predict the precise impact of climate change, but a recent slew of record hurricane seasons and temperatures -- such as the 2003 European heatwave that killed thousands of people -- suggested it would be a rough ride.